Buy film mail-order if you can't find it in a shop, after you have
inquired at a few labs if they will be able to handle it. Some machines
do, and some don't.

film example:
http://www.adorama.com/catalog.tpl?op=details&sid=10572612901019948&sku=K
KP400NC70

I know an aerial photographer who uses 70mm film a lot; works fine, and
it solves the film-changing problem with 12 exposures per film in a
plane with no door... and flying is expensive so you want to land with
as many good shots as possible.

Lourens